Tiny, ‘oxymoronic’ super-massive black hole discovered

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The accepted wisdom these days is that at the center of every galaxy in the universe lies a black hole — specifically, a super-massive black hole (SMBH). Galaxies are just the natural upshot of the formation of SMBHs, just as solar systems are the natural upshot of the formation of stars. Make a big enough gravity well, and things will start to fall into it. Now, however, NASA’s Chandra observatory has found an SMBH in the center of a distant galaxy, but it’s less than half the size of the previous smallest singularity found at the center of a galaxy.

Supermassive black holes are thought to form mostly by the melding of multiple small black holes, called seeds, or through the collapse of a truly enormous star. In order to have the gravitational attraction needed to get a large number of stars swirling around them, black holes need to be extremely massive — but perhaps occasionally less massive than previously believed. In the center of the galaxy RGG 118 is a black hole “just” 50,000 times the mass of the sun.

RGG 118.

The original X-Ray pulse that led to this discovery was picked up by the Chandra Observatory, but the visible-light measurements that actually revealed the mass of the center black hole came from Chile’s Clay Telescope.

RGG 118 sits about 340 million light years from the Earth, not terribly far by astronomical standards, so it can provide a case study for astronomers looking to understand how black holes form. For instance, though small, this SMBH conforms to prior observations about the relationship between black hole mass and the velocity of the swirling gas around it. RGG 118 is structured around a tiny, huge black hole, and it circulates more slowly than previously observed galaxies as a result.

Our own galaxy, the Milky Way, is believed to have a supermassive black hole at its center at a place called Sagittarius A, though that hasn’t been directly confirmed. The strongest evidence that exists right now, beyond the simple principle that all galaxies are built around singularities and there’s no reason to think that the Milky Way is any different, is an enormous burst of radiation detected from Sagittarius A in January of this year — more than 400 times as strong as normally recorded. Though it isn’t known quite what caused this, it is thought to be the result of something, perhaps an asteroid, getting pulled into a black hole.

The diversity of galaxies and their center objects is greater than previously imagined. Just a couple of years ago, scientists confirmed the existence of a galaxy 500 times smaller than the Milky Way, but revolving around a black hole several times larger than that in our own galaxy. There are many billions of galaxies, meaning that while there may be a great predisposition toward certain average galaxy forms, we are assumed to find many billions of statistical outliers too. Enormous super-galaxies, tiny dwarf-galaxies, and everything in between.

However, they all do seem to revolve around a black hole. The planets of our solar system wouldn’t stay together to form a system at all, if not for the Sun at the center, and the gasses of deep space wouldn’t come together to form a swirling mass like the Milky Way without an equally central force keeping it all together.

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